Impossible: comparing file contents with a speed that's faster than my slowest drive
- Posts: 2
- Joined: 28 Jan 2013
I'm a FreeFileSync user. Today, I used the file content compare option to check data integrity of my files. Something obviously went wrong, because there are many errors. However, I noticed that the speed at which the file content is compared is faster than the read speeds of my harddisks. Even equal files are compared at very high speeds. So, the software must cut corners, because one can never know the content of a file without reading it. Can someone tell me how this works? Thanks in advance... Tijs.
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- Site Admin
- Posts: 7058
- Joined: 9 Dec 2007
> I'm a FreeFileSync user
This is a quite awesome fact while posting on the FFS support forums. :)
> speed at which the file content is compared is faster than the read speeds of my harddisks
You're right, if FFS finds two files differ at the first few bytes it stops comparison and goes on with the next pair. However with regards to speed estimates it assumes it has processed the whole file. Thanks for this essential feedback. I have fixed this in the new release. When FFS finds two files differ it will only consider the actual bytes read up to this point for calculations of speed and remaining time. Here's the new version for testing:
[404, Invalid URL: http://freefilesync.sourceforge.net/FreeFileSync_5.12_beta_setup.exe]
This is a quite awesome fact while posting on the FFS support forums. :)
> speed at which the file content is compared is faster than the read speeds of my harddisks
You're right, if FFS finds two files differ at the first few bytes it stops comparison and goes on with the next pair. However with regards to speed estimates it assumes it has processed the whole file. Thanks for this essential feedback. I have fixed this in the new release. When FFS finds two files differ it will only consider the actual bytes read up to this point for calculations of speed and remaining time. Here's the new version for testing:
[404, Invalid URL: http://freefilesync.sourceforge.net/FreeFileSync_5.12_beta_setup.exe]
- Posts: 2
- Joined: 28 Jan 2013
I realised it myself, but you were ahead of me. In case of my files, the program can skip much data :(. (What did I do wrong? You copy from one disk to another, and apparently what you get is swiss cheese. Now I have to try to find out what is corrupted and what not. 350 GB of data... Shite.) I decided to be of assistance to you and test the modified program. Completely free of charge! ;) My data lends itself well for this purpose ;) And what I conclude is that the reported speed is more realistic now. Also, it still appears to skip remainders.
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- Site Admin
- Posts: 7058
- Joined: 9 Dec 2007
> What did I do wrong
Maybe there's something wrong with the hard drive. Just take two files that differ and compare them with a hex-editor. This way you will find out if the difference is data corruption or one side was changed in a legitimate way.
> My data lends itself well for this purpose
I know, therefore I was quick to provide you with an updated version to test before you fix your data. :)
Maybe there's something wrong with the hard drive. Just take two files that differ and compare them with a hex-editor. This way you will find out if the difference is data corruption or one side was changed in a legitimate way.
> My data lends itself well for this purpose
I know, therefore I was quick to provide you with an updated version to test before you fix your data. :)
